1. Field of the Invention
This invention relates to a control apparatus for a vehicular AC generator, in which the output voltage control of the vehicular AC generator is performed on the basis of a communication signal from a vehicle side ECU (engine control unit).
2. Description of the Related Art
In recent years, a conventional alternator for controlling the output voltage of a vehicular AC generator has been one in which the control value of the control voltage thereof is changed-over by a command value delivered from an external control unit such as ECU. Besides, control schemes for such a control voltage, presently in use, are broadly classified into the two schemes of “control-voltage two-stage control” and “control-voltage multistage control”.
The “control-voltage two-stage control” can change-over the control value of the alternator control voltage in two stages, and the control value usually consists of the two values of an ordinary voltage and a voltage lower than the ordinary voltage (refer to JP-A-6-261464 in detail).
The voltage lower than the ordinary voltage is used for suppressing a drive torque for the power generation of the alternator in order to enhance the startability of an engine or to enhance the acceleration performance of a vehicle, and it is changed-over to the ordinary voltage when the starting step of the engine or the accelerating step of the vehicle has ended.
On the other hand, the “control-voltage multistage control” can change-over the control value of the alternator control voltage in multistage fashion or linearly, and the operation of suppressing the drive torque in the engine starting mode or the vehicle accelerating mode as has been permitted by the two-stage control is made adjustable in multistage fashion here.
More specifically, the voltage (“LOW” side voltage) lower than the ordinary voltage in the two-stage control is usually set at respective set values which differ depending upon a vehicle skeleton, a battery, a vehicle service zone, a target fuel cost, etc. Moreover, orders for altering the factors are often made during the development of a vehicle. By way of example, even in the case of the two-stage control of an identical automobile manufacturer, orders in which the “LOW” side voltage has the different set voltage values of, for example, 12.4 V, 12.6 V and 12.8 V are given in accordance with individual vehicle sorts, and regulators which correspond to the set values are designed and mass-produced. However, when a request for altering the set value is received during the development of the vehicle, the design alteration of the regulator necessitates a huge cost, and the burden becomes heavy.
In contrast, in the case of the multistage control, a performance capable of controlling a range of, for example, 11-16 V in, for example, 128 stages is bestowed. When the automobile manufacturer utilizes the multistage control, the control value can be freely governed to a desired set voltage value very efficiently. Moreover, in the multistage control, the control value can be controlled to a set voltage value higher than the ordinary voltage. By way of example, therefore, the alternator power-generation voltage can be raised in a vehicle deceleration mode, thereby to rapidly charge the battery (as a regenerative control). Besides, the battery has a temperature characteristic in an efficient charging voltage value. In this regard, the ECU monitors the temperature of the battery so as to determine the optimum charging voltage and to give a command as the control value of the alternator control voltage, whereby the state of the battery can be held appropriate to prolong the lifetime thereof (refer to JP-A-7-194023 in detail).
As stated above, the two schemes of the “control-voltage two-stage control” and the “control-voltage multistage control” are used in the control devices of the alternators in the present situation, so that a signal operation within the ECU becomes greatly different depending upon which of the schemes is selected. Accordingly, the alteration of the control scheme at the stage of development or after the start of use results in forcing many design alterations or a burden in cost. By way of example, alternators being products in which designed different control devices A, B and C are mounted are naturally handled in different product names as the alternators A, B and C. Troublesomely a supplier and the automobile manufacturer make a stock management and an assemblage management for each of the different products.
Recently, the “control-voltage multistage control” with which the automobile manufacturer can freely alter and govern the control value without involving the design alterations has come into use. However, when either of the control schemes is to be selected at the initial stage of the development of a vehicle, the “control-voltage two-stage control” in the existing system is often selected with a priority given to safety. In addition, even if the study of the “control-voltage multistage control” has become necessary at the intermediate stage or final stage of the development, the estimation of the vehicle has proceeded from the physical viewpoint of a component constituting the control device of the alternator selected at the initial stage, and hence, the adoption of the “control-voltage multistage control” involving the alterations of respectively physically different components becomes a very difficult situation.